@Test public void testFindMessageByIdBad() throws MessagingException { Folder f = mock(Folder.class); target.mFolder = f; Message m1 = mock(Message.class); Message m2 = mock(Message.class); Message m3 = mock(Message.class); when(m1.getHeader(MESSAGE_ID_HEADER)).thenReturn(new String[] {"bleah"}); when(m2.getHeader(MESSAGE_ID_HEADER)).thenReturn(new String[] {"meh"}); when(m3.getHeader(MESSAGE_ID_HEADER)).thenReturn(new String[] {"three"}); when(f.getMessages()).thenReturn(new Message[] {m1, m2, m3}); Message message = target.findMessageById(WANTED_MESSAGE_ID); assertNull(message); }